Can you explain the phenomenon of stimulated emission in lasers?

[atmdw]

I am interested in learning the nature of the interaction between a photon and the atoms in a medium that has undergone population inversion that causes stimulated emission i.e. if an excited-state atom is perturbed by a photon (with an electric field of specific frequency), why does it emit an additional (amazingly) coherent photon? Specifically, what is the nature of the incident photon-excited state atom perturbation? If momentum transfer, how is momentum transferred without change to the incident photon?
Thanks
An ignorant chemist

 

[mathman]

http://en.wikipedia.org/wiki/Stimulated_emission

Try the above.

 

[atmdw]

I have read the Wikipedia entry numerous times and it is informative (as is other web-based info). Wiki author states "When light of the appropriate frequency passes through the inverted medium, the photons stimulate the excited atoms to emit additional photons of the same frequency, phase, and direction, resulting in an amplification of the input intensity". My question is how does an incident photon (some of which presumably are not absorbed) induce additional photon emission from excited state atoms. I have read that there is some type of momentum transfer but I don't understand how that occurs without a change in energy (and frequency and phase) in the incident photon. A few good articles (but surprisingly few publications) are available on coherence but the conservation of momentum argument is confusing to me. I'm presuming that Einsteins thought experiment didn't involve a photon drive by.

 

[mathman]

I suggest you try to get a modern description of the physics described in Einstein's paper. I have never gone through it, but simply accepted it as a fact of nature (lasers work!).